Physiological development in plants is impacted by environmental conditions, with moisture and heat being of primary importance. Economically important crops such as corn and soybeans are categorized and evaluated on the basis of the amount of heat required to reach various development stages. For example, a specific corn hybrid requires a certain amount of heat to emerge, flower and reach physiological maturity (black layer). A different hybrid may require more or less heat for similar development. The warmer the average temperature, up to a maximum, the faster corn grows. The amount of heat accumulated during the growing season is measured as “growing degree units” (GDUs).
Growing degree units are used in the industry to describe and predict stages of corn growth from planting to harvest. It is also a common practice in the industry to develop various GDU requirements for particular hybrid products. The majority of all seed companies use GDUs as part of their product description and the GDU calculation set forth below is an industry standard. These GDU ratings are used by seed professionals and growers to select their product portfolio, and are used to assist growers to spread their production risks. For example, selecting hybrids with different flowering/silking GDU requirements will offer some protection during an unexpected midsummer period of high heat. GDUs are also used in seed production to determine inbred split planting times. Weeds and insect pest cycles are also impacted by GDUs.
Knowing how much heat has accumulated on a daily basis helps growers monitor their crop development and make management decisions that optimize crop performance. Traditionally, farmers obtain accumulated GDU data calculated from temperature readings taken at a site located in a region where the farmers' fields or growing sites are located and compare the GDU data to the historical GDU data for that region. Farmers obtain the GDUs accumulated year to date for a particular region from the local newspaper, television, and/or radio. Typically, this information includes whether the accumulated GDUs are ahead or behind a “normal” year for region in which the farm site is located. A farmer may use this regional information to determine crop management strategies at his particular fields for that particular growing season. In the U.S. Midwest, accumulation of GDUs typically begins on April 1st and ends on October 1st.
The GDU data available to the farmer from public sources are likely calculated based on a start date that is different from the date farmers plant their fields. A farmer located in the northern portion of a region may experience significantly more rain than farmers located in the southern portion, causing that farmer to delay planting by two weeks compared to his or her southern counterparts. Thus, the GDU data available from the newspaper, radio, etc. in many cases will not accurately reflect the GDUs that actually impinge on a farmer's particular field.
Furthermore, regardless of the differences between data collection start dates, GDUs vary significantly within a county or region and among different farm sites in a region. Thus, the GDU data available from the newspaper, radio, etc. will not likely reflect the GDU accumulation at a farmer's local site. Variations in GDU accumulation can have a significant effect on crop performance and, therefore, crop management strategies. Inaccurate GDU data may lead the farmer to apply incorrect or sub-optimum crop management strategies.
Therefore, there is a need to take temperature readings at a farmer's field, accurately calculate the actual accumulated GDUs that impinge on a farmer's crops, and to compare current accumulated growing season GDUs at the particular site with historical data from the same site. There is also a need to provide a small, reliable and inexpensive GDU meter for placement in or adjacent to a farm site for this purpose. There is a further need to provide accurate crop management strategies to the farmer based upon the amount of GDUs accumulated at a particular site.